Electric arc furnace



Nov. 21 1944. NIS IM 2,363,078

ELECTRIC ARc FURNACE Filed April 30, 1943 3 Sheets-Sheet l Nov. 21, 1944. Nl m 2,363,078

ELECTRIC ARC FURNACE Filed April 30, 1943 3 Sheets-Sheet 2 Rn: Zuun /WM MQ.

Nov. 21, 1944. R. N|ss|M 2,363,078

ELECTRIC ARC FURNACE Filed April 30, 1943 3 Sheets-Sheet 3 Patented Nov. 21, 1944 OFFICE ELECTRIC ARC FURNACE Raoul Nissim, London, England Application April 30 1943, Serial No. 485,135

In Great Britain May 22, 1942' 7 Claims.

The present invention relates to an electric arc furnace, and is particularly concerned with apparatus for ensuring that good electric contact is made between each electrode and the leads carrying the current thereto.

In present day electric arc furnaces each electrode is normally cased within a sheath. The sheath'is sealed to the electrode over its upper part whilst the lower part encloses one or more clamps constituting electric connectors to the electrode. Electric current leads to the clamps are taken through the sheath, the bottom end of which passes into the furnace in a gas-tight manner through cooling rings disposed around the aperture in the furnace roof. One form of known clamping device comprises a screw-driven wedge operated between the sheath and the clamp.

Such an arrangement suffers from the disadvantages that owing to deformation of the furnace roof with the changes of temperature it is difficult to preserve the gas tight seal at the point where the sheath passes through the cooling rings. Furthermore, since the lower part of the sheath and the clamps within it lie within the furnace, if the clamps are operated by springs or screws the heat of the furnace damages these members and as they are close to the furnace, hand operation of these members is difficult and entails an interruption of the current with a consequent loss of production.

In another arrangement the electric current leads are connected to the sheath itself, the lower end of which may dip into a sand seal formed on the furnace roof. In this arrangement it is difiicult to ensure adequate contact between the sheath and the electrode in the absence of means for pressing the sheath upon the electrode.

It is known to form self-baking electrodes in a sheet steel mould of a plurality of part-cylindrical sections which adapt themselves well both to the shape of the electrode and to the sheath. It frequently occurs, however, that the baked paste extrudes between the sections of the mould and tends to stick against the external casing which again gives rise to considerable trouble.

It is an object of the present invention to provide means whereby the above mentioned difliculties may be avoided.

According to the present invention there is provided an electric hearth furnace comprising a hearth; a roof; an electrode extending into the hearth through an aperture in the roof; an electrode-sheath located wholly above the roof sealed loosely to the top of the roof and sealed to the electrode at a point well above the roof but being spaced from the electrode for a portion of its length intermediate said two seals; a clamp; and, extending through the sheath to the clamp,

' an electric current lead to the clamp and means Figures 2, 3, 4, 5 and 6 are sectional elevations of alternative embodiments of the present inven- 7 tion, whilst Figure 7 is a composite transverse section illustrating further embodiments of the invention.

In the arrangement illustrated in Figure 1 it is assumed that the electrode is stationary and that changes of the arc current are effected by changing the supply voltage. In this arrangement the electrode and its sheath are mounted upon a common fixed support which is independent of the furnace roof, whilst clamps and their cooperating means aresupported by the sheath.

Referring to this figure, a fixed electrode [0 is partly encased by a sheath l2 which at its upper end is sealed to the electrode with tar or pitch so as to make a gas-tight seal at a position well above the furnace roof and thus well away from great heat. The lower end of the sheath I2 is formed with a water-cooled ring l3 and with a flange l4 dipping into a trough l5 formed on the furnace roof l6 and filled with sand I! or the like. The electrode I0 and its sheath l2 are suspended as at It by means independent of the furnace roof so that deformations of the latter, due to changes of temperature, do not break the seal ll between the electrode and the roof.

Between the upper and lower seals are disposed a plurality of clamps one of which is shown at [9. Each clamp is located within the sheath I2 and electric current leads 2!] to each clamp are passed in a gas-tight manner through the sheath. The clamp operating means which are shown also in the bottom left hand quarter of Figure 7 comprise a rod 2| passing freely through the sheath to which is secured a wedge 22 against which bears an adjustable screw 23. Pressure can be brought to bear upon the clamp by manand 33 respectively is to the chamber therefrom by pipe 48.

ual adjustment of the screw 23 but normally the pressure on the clamp is adjusted by rotation of an auxiliary ring 24 secured within a ring on the sheath. It will be seen that rotation of the ring 24 in the direction of the arrow 26 (Figure '7) is effective to increase the pressure on the clamp whilst rotation of the ring 24 in the opposite angular sense reducesthe pressure on the clamp. g

As shown at the right hand side of Figure 7 rotation of the ring 24 is controlled hydraulically course move with the by means of a differential piston 21 working By means of the pipe 29 supplied to both sides within the cylinder 28. fluid at constant pressure is of the difierential piston 21 whilst the escape of fluid from the upper side of the piston is controlled by means of a valve 30. ring 24 is linked with the piston 21 as illustrated so that, by controlling the valve 39, the

adjust the pressure applied. to each clarnp asso ciated with each electrode. v

The resultant pressure above and below the piston 21 is rotate the ring 25 in the direction. which increases pressure upon theclampscso that the system is automaticallyself-locking.v

the auxiliary ring from control means, such as the-hydraulic means illustrated in Figure 7, located at a distanc'eirom: the'electrode.

The screw 23 may be provided at its lower end with a wedge 3| as illustrated at the top left hand side of Figure 7. Alternatively, both wedges may The auxiliary f ring 2 3 can be rotated in their direction in order to sheath.

As illustrated in Figures 1 to 5 inclusive, each clamp is suspended from the sheath and the sheath is suspended independently of the furnace roof.

In the arrangement illustrated in Figure 6 it is assumed that the strength of the arc current is varried by varying the position of the electrode axially with respect to the molten metal. For this purpose the electrode is made movable with respect to its sheath whilst the clamp must of electrode. Thus, the sheath and the operating means for the clamp are stationary whilst the electrode and the clamp move axially. The clamp operating means are supported upon the sheath. The sheath is suspended independently of the room and each clamp is suspended independently of both the roof and Furthermore, pressure is exerted upon each clamp I9 by way of a roller 49 so that both the clamp and the electrode may be moyed without releasing the pressure uponthe clampQthis arrangementbeing of special advantagewhere such that. ifthe exhaust pipe breaks the piston 21 moves downwardly-thus tending to the height of the electrode above the bath is controlled automatically in accordance with changes of arc current. Pressure is appliedto the clamp in a manner similar to that illustrated in Figure 5. Thev upper part. of the sheath I2 .is sealed to the electrode =l0, whilst the lower end of the sheath is formed with a cooling ring .50 and a flange 5l dipping into a sandseal 52 formed either in the furnace root H5 or on an auxiliary be omitted in which case the screw;23 bears di-j rectly againstthe'clarnp 1-9 as shown at the right hand side of Figure 7, the clamp having an eccentricrib 33, as shown. I

1 Figure 2 illustrates another embodiment of the invention suitable fore, the electrode sheath l-2 which at 10 is partly "enclosed within a itsupper and lower ends 32 sealedto the electrode in, whilst the lower end 33 isiormed with a-flange 33A dipping-into a sand seal 333 formed in the furnace-roof l6. Pressure upon or down upon a rod 35 by tation of the latter each clamp l is exerted by means of a wedge member iii lwhich for a fixed electrode. As be ring resting upon the furnace roof. The seal 5.2, being of annular shape, hasthe advantageover the seal 1H illustrated in Figure 1, that sand .does not tend to drop into the furnace. Referring again to Figure 6, it will beseen that-the clamp I9 is suspended from a beam 53 by way of arod 54; the beam being adjustable in height by apparatus illustrated at 55. The height -:of the-electrode I0 is adjustable by apparatus illustrated at 56, whilst the sheath'tIZ is fixedly suspended from a platform 51.

, ,In all forms of the invention'illustrated sufficient space mustbeleftbetweenthe sheath and the electrode for lateral adjustment of the clamps. I

' If desired the sheath-may besnaturallyor wartificially cooled over the whole of its len th.

I claim:

1. An electric furnace comprising a hearth; .a roof; an {electrode extending into the hearth through an aperture in the roof .an electrode- The electrode 10,.togetherwith its sheath 1-2,

are mounted upon a common fixed support l8.

In Figure 3 is illustrated a similar arrangement except that pressure is exerted upon the clamp I9 by rotation of the rod 35 to move the rack '38 co-operating with a pinion v35. to rotate thescrew 23. g

As illustratedin'Figure 4, pressure upon the clamp I9 'is exerted by-means of apair-of wedges 40 and "41, whilst, as illustrated in-Figure 5, pressure upon the clamp I9 is exerted by means of.

a spring located between a pair ofpistons 83 and "M, the latter of which is adjustable in position by means of a screw pressing the former piston 43 against the clamp 19. Fluid is supplied When it is desired to alter the pressure on the clamp or to release it the 'fluid control being used for the normal clamping and unc'lamping, whilst adjustment. of the screw-1 H5 is used to adjust the final clamping pressure.

46 by a pipe 4'! and exhausted 1 sheath located wholly above the roof sealed loosely to the top ;.of the roof and sealed to the electrode at a point -well-above the roof but being spacedtrom the electrode ;for a portion of its length intermediatessaiditwoseals; a clamp; and, extending through the sheath to the .01amp, an 'electric current lead to the clamp :and .;means for operating said clamp.

2. A furnace asclaimed iniclaim :1, comprising a trough-like seal on the .furnacezroof into which dips the sheath.

.3. A furnace as claimed. in claim vl,.:comprising an axially movable electrode,aa-:movable support for the electrode v and itsclamp, and :-afixed sup- .port independent of the roof ,fortheusheath'and the clamp-operating means.

4. A furnace as claimed in claim "1, wherein each electrodeis providedwith a plurality of clamps and :eachclamp .is jprovided withseparate -c1amp-operating :means comprising .a wedge, therebeing zalsoprovided -a-;'rotatab1e :aux-iliary ringisurrounding the clampsand carrying clampoperating means, one of which is adapted to engage each clamp wedge, the arrangement being such that upon rotation of the auxiliary ring in one angular direction pressure upon the clamps is increased, and upon rotation of the ring is the other angular direction pressure upon the clamps is reduced.

5. A furnace as claimed in claim 1, wherein each electrode is provided with a plurality of clamps and each clamp is provided with separate clamp-operating means comprising a wedge, there being also provided a rotatable auxiliary ring surrounding the clamps and carrying clampoperating means one of which is adapted to engage each clamp wedge, and fluid operated mechanism for rotating said auxiliary range, the arrangement being such that upon rotation of the auxiliary ring in one angular direction pressure upon the clamps is increased, and upon rotation of the ring in the other angular direction pressure upon the clamps is reduced.

6. A furnace as claimed in claim 1, wherein each electrode is provided with a plurality of clamps and each clamp is provided with separate clamp-operating means comprising a wedge, there being provided also a rotatable auxiliary ring surrounding the clamps and carrying clamp-operating means one of which is adapted to engage each clamp wedge, and fluid operated mechanism for rotating said auxiliary ring including a differential piston and cylinder to the opposite sides of which fluid is supplied at constant pressure, and from one side of which fluid is exhausted at a rate which is varied when it is desired to change the pressure applied to the clamp, the piston being connected with the auxiliary ring, the arrangement being such that upon rotation of the auxiliary ring in one angular direction pressure upon the clamps is increased, and upon rotation of the ring in the other angular direction pressure upon the clamps is reduced,

7. A furnace as claimed in claim 1, wherein said clamp operating means comprises a roller, and means for urging the roller against the clamp so that pressure may be applied to the clamp whilst the electrode is moved.

RAOUL NISSIM. 

